Discrimination between poultry eggs on the basis of some observable quality is a well-known and long-used practice in the poultry industry. “Candling” is a common name for one such technique, a term which has its roots in the original practice of inspecting an egg using the light from a candle. As is known to those familiar with eggs, although egg shells appear opaque under most lighting conditions, they are in reality somewhat translucent, and when placed in front of a direct light, the contents of the egg can be observed.
An egg may be a “live” egg, meaning that it has a viable embryo. FIG. 1A illustrates a live poultry egg 1 at about day one of incubation. FIG. 1B illustrates the live egg 1 at about day eleven of incubation. The egg 1 has a somewhat narrow end in the vicinity represented at 1a as well as an oppositely disposed broadened end portion in the vicinity shown at 1b. In FIG. 1A, an embryo 2 is represented atop the yolk 3. The egg 1 contains an air cell 4 adjacent the broadened end 1b. As illustrated in FIG. 1B, the wings 5, legs 6, and beak 7 of a baby chick have developed.
An egg may be a “clear” or “infertile” egg, meaning that it does not have an embryo. More particularly, a “clear” egg is an infertile egg that has not rotted. An egg may be an “early dead” egg, meaning that it has an embryo which died at about one to five days old. An egg may be a “mid-dead” egg, meaning that it has an embryo which died at about five to fifteen days old. An egg may be a “late-dead” egg, meaning that it has an embryo which died at about fifteen to eighteen days old.
An egg may be a “rotted” egg, meaning that the egg includes a rotted infertile yolk (for example, as a result of a crack in the egg's shell) or, alternatively, a rotted, dead embryo. While an “early dead”, “mid-dead” or “late-dead egg” may be a rotted egg, those terms as used herein refer to such eggs which have not rotted. Clear, early-dead, mid-dead, late-dead, and rotted eggs may also be categorized as “non-live” eggs because they do not include a living embryo.
Eggs which are to be hatched to live poultry are typically candled during embryonic development or later to identify clear, rotted, and dead eggs (collectively referred to herein as “non-live eggs”) and remove them from incubation to thereby increase available incubator space. U.S. Pat. Nos. 4,955,728 and 4,914,672, both to Hebrank, describe a candling apparatus that uses infrared detectors and the infrared radiation emitted from an egg to distinguish live from infertile eggs.
U.S. Pat. No. 4,671,652 to van Asselt et al. describes a candling apparatus in which a plurality of light sources and corresponding light detectors are mounted in an array, and wherein eggs are passed on a flat between the light sources and the light detectors.
Other applications where it is important to be able to distinguish between live and non-live eggs are becoming important. One of these applications is cultivation and harvesting of human flu vaccines via live eggs. Human flu vaccine production is accomplished by injecting seed virus into a chicken egg at about day eleven of embryonic development (day-11 egg), allowing the virus to grow for about two days, euthanizing the embryo by cooling the egg, and then harvesting the amniotic fluid from the egg.
Typically, eggs are candled before injection of a seed virus to remove non-live eggs. The fluid surrounding virtually all early and mid-dead eggs in many hatcheries tend to have a white, milky appearance and are referred to in the industry as “milky” eggs. It is surmised that the procedure of washing an egg prior to incubation may produce a milky egg either by the wash solution transporting pathogens into the egg or because the washing removes some of the protective cuticle on the egg shell. Unfortunately, the embryo of a Day-11 egg may block as much light from a candling apparatus as a milky egg. As a result, it may be difficult to distinguish between milky early dead eggs and live eggs at this stage of embryonic development.